sedimentary

Limonite (Ironstone)

Hydrated Iron(III) Oxide-hydroxide (FeO(OH)·nH2O)

Hardness: 4 to 5.5 (Mohs scale), Color: yellowish-brown to dark brown, Luster: dull to earthy (sometimes sub-metallic or vitreous when wet/smooth), Crystal Structure: Amorphous (microcrystalline), Cleavage: absent

Hardness: 4 to 5

Identified July 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed in the oxidation zone of iron-rich mineral deposits or as a chemical precipitate in shallow marine, lacustrine, or bog environments. These specimens often originate from the Paleozoic or Mesozoic eras. It often forms through the weathering of other iron minerals like pyrite or magnetite.

Uses & applications

Historically used as a minor ore of iron; commonly used as a pigment (brown ochre) for paints and dyes. Primarily of interest to geological collectors today.

Geological facts

Limonite is not a single mineral but a mixture of hydrated iron oxides, primarily goethite. It is responsible for the deep orange and brown colors of Many soils and rusty rock faces worldwide.

Field identification & locations

Identify by its characteristic yellowish-brown streak when rubbed on unglazed porcelain. It is commonly found in sedimentary rock beds, bog deposits, and weathered outcrops of metal deposits. Often heavy for its size due to iron content.

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